The present invention relates to an apparatus and method for using ultrasound augmented with microbubbles, thrombolytic drugs or other lysing agents for clot lysis, and in particular to such an apparatus and method using time, phase and frequency modulation of multiple acoustic signals from one or more ultrasound transducers to provide uniform power delivery with fewer gaps in the ultrasound field.
Thrombosis is the development of a blood clot within a blood vessel. A thrombosis can cause serious, even life threatening, conditions due to partial or total blockage of a blood vessel. Various techniques are known for lysing or removal of the clot. These techniques include the injection of various clot dissolving agents.
Ultrasound has been found to be useful in lysing clots and enhancing the effectiveness of a lysing agent, such as a thrombolytic drug.
More recently, microbubbles have been found to be effective as a lysing agent when used in conjunction with ultrasound. Microbubbles are used in the form of a liquid containing stable microspheres of an insoluble, preferably inert, gas. However, conventional techniques are limited in the size and range of the ultrasound field and suffer from gaps in the field and shadowing caused by differential propagation of the ultrasound field through various shapes, compositions and densities of anatomical structures.
U.S. Pat. No. 6,514,220, the disclosure of which is incorporated herein by reference, discloses that the effect of ultrasound irradiation of a portion of a human or animal body is enhanced by operating a portion of the human or animal body as a trapped mode resonator.
The prior art teaches focusing or concentrating ultrasound energy. However, ultrasound energy focused or concentrated at a single location may produce excessive heating or cavitation, particularly when the acoustic field is static. Static acoustic fields may also suffer from insufficient energy levels or gaps in portions of the field.